The present disclosure relates to a developing device incorporated in an image forming apparatus exploiting electrophotography, such as a copier, a printer, a facsimile machine, a multifunction peripheral thereof, etc., and to an image forming apparatus incorporating such a developing device. More particularly, the present disclosure relates to a developing device which can be replenished with fresh two-component developer containing toner and carrier and can meanwhile discharge surplus developer, and to an image forming apparatus incorporating such a developing device.
In an image forming apparatus, a latent image formed on an image carrying member comprising a photosensitive member or the like is made visible by being developed into a toner image by a developing device. Some such developing devices adopt a two-component developing system that uses two-component developer. In this type of developing device, two-component developer (hereinafter, also referred to simply as developer) containing carrier and toner is stored in a developer container, there is arranged a developing roller which feeds the developer to the image carrying member, and there is arranged a stirring member which transports, while stirring, the developer inside the developer container to feed it to the developing roller.
In the developing device, toner is consumed in developing operation, while carrier is left unconsumed in the developing device. Thus, the carrier stirred together with toner inside the developer container deteriorates as it keeps being stirred repeatedly, gradually diminishing the toner charging performance of the carrier.
As a solution, developing devices have been proposed that supply fresh developer containing carrier into a developer container while discharging surplus developer so as to suppress degradation in charging performance.
For example, a known developing device based on a system in which fresh carrier and toner are supplied into a developer container includes a first transport portion which transports developer inside a developer container, a second transport portion which is arranged on the downstream side of the first transport portion with respect to the transport direction thereof and which is formed by a helical blade spiraling in the opposite direction so as to transport developer in the opposite direction to the first transport portion, a disk portion arranged on the upstream side of the second transport portion with respect to the transport direction thereof, and a third transport portion which is arranged on the upstream side of the disk portion with respect to the transport direction of the second transport portion, for transporting developer into a developer discharge port. In the developing device, the disk portion and the helical blade of the second transport portion are arranged across a gap.
With the above configuration, as fresh developer is supplied into the developer container, the developer is, while being stirred, transported to the downstream side of a transport chamber by rotation of the first transport portion. As the reverse helical blade of the second transport portion rotates in the same direction as the first transport portion, a transport force is applied to the developer in the opposite direction to the developer transport direction by the first transport portion. By the transport force in the opposite direction, the developer is blocked, and increases its height; thus surplus developer moves over the second transport portion and the disk portion (regulating portion) into the developer discharge port and is discharged to the outside. Moreover, an end part of the helical blade of the second transport portion and the disk portion are arranged so as not to be joined to each other so as to stabilize the height of the developer inside the developer container.